This project focuses on the molecular mechanisms that regulate the insulin-like growth factor I receptor (IGF1R). Constitutive or inappropriate activation of many tyrosine kinases plays a role in the progression and development of various forms of human cancer. Recent evidence has implicated IGF1R in malignant transformation, and IGF1R has emerged as a target for anticancer drug design. No clinically effective inhibitors for IGF1R have been developed to date. Aim 1 studies the mechanism of IGF1R autophosphorylation. Upon ligand binding, IGF1R is activated by phosphorylation at three sites in the activation loop of the kinase catalytic domain. We will determine the functional significance of each phosphorylation using biochemical, biophysical, and computational approaches. Aim 2: In collaboration with Dr. Stevan Hubbard, we recently determined a dimeric structure of IGF1R which potentially represents an intermediate in the autophosphorylation process. We will carry out biochemical and cell biology experiments to test this possibility. The dimeric structure may also explain the effect of an Arg-to-Gln mutation in insulin receptor observed in two patients with non-insulin- dependent diabetes. Aim 3 will explore the hypothesis that the juxtamembrane region of IGF1R is involved in autoinhibition. We will study juxtamembrane mutants in fibroblasts derived from IGF1R-deficient mice. We will also analyze the purified proteins using biochemical and structural approaches.